You walk into the bathroom and are hit by a pungent, rotten-egg smell. Or you smell something foul in the kitchen that isn’t coming from the trash. A sewer smell in your home is more than just annoying. It could indicate a problem with your sewer system that needs attention. And in some cases, it’s also unhealthy: sewer gas contains hydrogen sulfide and methane, among other things.
In this article, we explain where sewer odors come from, what the six most common causes are, and what you can do about them.
Where does sewer odor come from?
Your sewer system is designed to drain wastewater without you even noticing. Every drain in your home (sink, shower, toilet, washing machine) has a trap: a bend in the pipe that always holds a small amount of water. This water seal prevents odors from the sewer from entering your home.
If you smell a sewer odor, something has gone wrong somewhere in the system. The water seal is no longer working, there’s a leak in the pipe, or there’s a clog that’s pushing gases back toward your home.
The 6 most common causes
1. Dry water seal
This is the most common cause—and fortunately, also the easiest to fix. If you don’t use a drain for an extended period (such as a guest bathroom toilet, a utility room sink, or a floor drain in the garage), the water in the trap evaporates. Without that water seal, there is an open connection between the sewer and your home.
Solution: Let water run for a few minutes in any drain you don't use regularly. Do this at least once every two weeks. The trap will refill, and the odor will disappear immediately.
2. Clog in the drainpipe
A (partial) blockage in your sewer can prevent gases from escaping properly through the vent pipe on the roof. Instead, they are forced back through your drain pipes and enter your home through the weakest points.
Do you notice gurgling sounds or water draining slowly, in addition to the odor? If so, a clog is likely the cause.
Solution: For a simple clog, you can clean the trap or try using a plunger. If that doesn't work, or if multiple drains are slow, have a professional unclog the pipe.
3. Defective or missing odor trap
Sometimes a drain trap is broken, installed incorrectly, or missing altogether. This can happen during DIY renovations, in older homes, or after work done by a plumber who didn’t finish the job properly.
You can tell if a trap is broken because you can smell the sewer odor constantly, whether you're running water or not.
Solution: Have the odor traps inspected and replaced if necessary. This is a relatively simple job for a professional.
4. Problem with the venting
Every sewer system has a vent pipe, usually a pipe that extends outside through the roof. This pipe ensures that the air pressure in the sewer system remains balanced. If this pipe becomes clogged (by leaves, a bird’s nest, or ice in the winter), negative pressure builds up in the pipes. This negative pressure sucks the water out of your trap, causing the odor barrier to disappear.
Solution: Check to see if the vent pipe on the roof is clear. Can't reach it, or are you unsure? A technician can check this quickly.
5. Crack or break in the sewer line
Even a small crack in your sewer pipe is enough to allow sewer gas to seep into your home. You’ll often notice the smell in specific areas: near a wall, in the crawl space, or in the basement. The odor can vary depending on the temperature and humidity.
A break in a pipe is harder to locate because the pipe is usually hidden under the floor or buried in the ground. Using smoke detection, a specialist can pinpoint the exact location of the leak. Harmless smoke is blown into the pipe; wherever the smoke escapes, that’s where the problem is.
Solution: Have an inspection performed. Depending on the severity of the problem, the pipe can be repaired, or sewer relining may be the best option.
6. Sewer odor from outside
Sometimes the sewer odor doesn’t come from your own sewer system but from outside. An overloaded municipal sewer system, construction work on the street, or a blockage in your neighborhood’s main sewer line can cause sewer odors to escape into the air through manhole covers or street drains. That odor then enters your home through open windows or ventilation grilles.
Solution: Temporarily close the windows and vents on the side where the odor is coming in. Contact your local government if the problem persists.
Sewer smell after a renovation
A common situation: you’ve just finished renovating, and suddenly you smell a sewer odor in your home. This is almost always caused by one of these three reasons:
- Missing odor trap: An odor trap was not installed (or reinstalled) when the pipes were modified.
- Damaged pipe: During the renovation, a pipe was accidentally hit or moved.
- Vent closed off: the vent pipe has been bricked up, cut off, or connected to a range hood (which is not permitted).
Always have your sewer system inspected after renovations if you smell a foul odor. The sooner you address the issue, the less damage and inconvenience there will be.
Is sewer gas in the house dangerous?
In small quantities, sewer gas is mainly a nuisance. However, prolonged exposure or exposure in enclosed spaces (crawl spaces, basements) can pose risks:
- Hydrogen sulfide (H₂S): the gas that causes that rotten-egg smell. In high concentrations, it can cause headaches, nausea, and dizziness.
- Methane: is flammable. In a poorly ventilated area, the accumulation of methane could theoretically pose a fire hazard.
- Bacteria and mold: Moisture from a leaking sewer pipe promotes mold growth, which can cause respiratory problems.
If you notice a persistent sewer odor, especially in bedrooms or living areas, it’s a good idea to have the problem fixed as soon as possible.
When should you call a specialist?
Does running water down all the drains not help? Then the problem runs deeper, and you need professional help. Especially in these situations:
- The smell is always there, not just now and then
- You can smell it in several places around the house
- The smell started after a renovation
- Do you also have clogged drains or gurgling pipes?
- There is visible moisture or water in the crawl space
At RBNL, we come out to inspect the issue and resolve it on-site whenever possible. We offer fixed-price services, operate on a " no cure, no pay " basis, and are available 24/7.
Having trouble with sewer odors? Contact us →
Frequently Asked Questions About Sewer Odors in the Home
Why do I smell sewage when it rains?
Heavy rain can overload the sewer system. This causes gases to be forced back toward homes. Rainwater can also drain the water traps if the venting system isn’t working properly. Is this happening more often? Have your sewer system inspected.
Can sewer odors come through the wall?
Yes. A crack in a sewer pipe that runs through or along a wall can cause sewer gas to seep through the masonry into the building. Smoke detection can help pinpoint the exact location.
Does an air freshener or scented candle help mask sewer odors?
No. An air freshener just masks the odor; it doesn't solve the problem. The cause lies in your sewer system and needs to be addressed there. Don't just put up with a smelly house—find the source.
How much does it cost to eliminate sewer odors?
That depends on the cause. You can fix a dry water trap yourself at no cost. Replacing a broken trap costs very little. RBNL charges a flat rate for camera inspections or smoke detection. Check our price list for current rates.
I only smell sewage in the morning—how is that possible?
Sewer odors can be stronger when there are temperature fluctuations. In the morning, as the house warms up, air rises more quickly from the pipes. Inactivity at night (when no one is using water) can also cause the water seal to drop. Let the water run briefly in all drains in the morning.
